Low profile, high stretch, low dilation knit prosthetic device

ABSTRACT

A radially expandable stent-graft endoprosthesis is provided. The graft included in the stent-graft is a knitted tubular structure circumferentially disposed and securably attached to the stent. The knitted tubular structure has a warp knit pattern of interlacing yarns with at least a two-needle underlap to provide greater than 150 percent longitudinal stretchability while substantially inhibiting dilation. A knitted tubular graft and a knitted medical fabric with greater than 150 percent longitudinal stretchability are also provided.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. application Ser. No.09/898,103, filed Jul. 3, 2001, the contents of which are incorporatedherein by reference.

FIELD OF INVENTION

[0002] The present invention relates generally to a tubular implantableprosthesis having a knitted textile structure. More particularly, thepresent invention relates to an endoprosthesis with a knitted textilestructure having increased longitudinal stretchability and furtherhaving radially restricted enlargement.

BACKGROUND OF RELATED TECHNOLOGY

[0003] An intraluminal prosthesis is a medical device used in thetreatment of diseased blood vessels. An intraluminal prosthesis istypically used to repair, replace, or otherwise correct a diseased ordamaged blood vessel. An artery or vein may be diseased in a variety ofdifferent ways. The prosthesis may therefore be used to prevent or treata wide variety of defects such as stenosis of the vessel, thrombosis,occlusion or an aneurysm.

[0004] One type of intraluminal prosthesis used in the repair ofdiseases in various body vessels is a stent. A stent is a generallylongitudinal tubular device formed of biocompatible material which isuseful to open and support various lumens in the body. For example,stents may be used in the vascular system, urogenital tract and bileduct, as well as in a variety of other applications in the body.Endovascular stents have become widely used for the treatment ofstenosis, strictures and aneurysms in various blood vessels. Thesedevices are implanted within the vessel to open and/or reinforcecollapsing or partially occluded sections of the vessel.

[0005] Stents generally include an open flexible configuration. Thisconfiguration allows the stent to be inserted through curved vessels.Furthermore, this configuration allows the stent to be configured in aradially compressed state for intraluminal catheter implantation. Onceproperly positioned adjacent the damaged vessel, the stent is radiallyexpanded so as to support and reinforce the vessel. Radial expansion ofthe stent may be accomplished by inflation of a balloon attached to thecatheter or the stent may be of the self-expanding variety which willradially expand once deployed. Structures which have been used asintraluminal vascular grafts have included coiled stainless steelsprings; helically wound coil springs manufactured from a heat-sensitivematerial; and expanding stainless steel stents formed of stainless steelwire in a zig-zag pattern. Examples of various stent configurations areshown in U.S. Pat. Nos. 4,503,569 to Dotter; 4,733,665 to Palmaz;4,856,561 to Hillstead; 4,580,568 to Gianturco; 4,732,152 to Wallstenand 4,886,062 to Wiktor, all of whose contents are incorporated hereinby reference.

[0006] A graft is another commonly known type of intraluminal prosthesiswhich is used to repair and replace various body vessels. A graftprovides a lumen through which blood may flow. Moreover, a graft isoften configured to have porosity to permit the ingrowth of cells forstabilization of an implanted graft while also being generallyimpermeable to blood to inhibit substantial leakage of bloodtherethrough. Grafts are typically tubular devices which may be formedof a variety of materials, including textile and non-textile materials.

[0007] A stent and a graft may combined into a stent-graftendoprosthesis to combine the features thereof. The graft, however, inthe stent-graft endoprosthesis should comply with the implantationrequirements of the stent which often include collapsing the stent forplacement at an implantation site and expansion of the stent forsecurement thereat. Grafts which cannot easily accommodate thelongitudinal and/or radial dimensional changes from a unexpanded orcollapsed state to an expanded stent often complicate the implantationof the stent-graft. For instance, some grafts are folded in thecollapsed or unexpanded state and must be subsequently be unfolded toaccommodate the expanded stent. The unfolding of the graft, however,often complicates the placement of the graft on the stent and theimplantation of the stent-graft itself. Alternatively, noncontiguousgrafts have been used with expandable stent-grafts. Upon expansion ofthe stent, however, portions of the noncontiguous graft often separateto accommodate the stent expansion. This separation leaves gaps in thegraft structure thereby permitting the leakage of blood through thesegaps.

[0008] Moreover, an intraluminal device, such as a stent, a graft or astent-graft, may dilate over time after implantation within a bodilylumen. The dilation of the implanted intraluminal device is a radialenlargement of the device resulting from pulsating stresses or pressurespresent within the bodily lumen. The action of the pulsating stresses orpressures often fatigue the structure of the device resulting in radialexpansion and possibly longitudinal foreshortening.

[0009] A variety of mechanical means have been used to attempt to limitdevice dilation. For example, U.S. Pat. No. 5,843,158 to Lenker et al.describes the use of generally inelastic frame rings circumferentiallydisposed along a radially contractible stent-graft. The frames aredescribed as limiting the radial expansion. Such frames, however, mustbe integral to the-stent and complicate the stent-graft geometry.

[0010] U.S. Pat. No. 5,843,158 to Lenker et al. further describesmechanical means for limiting radial expansion of a graft in astent-graft. In one alternative, the stent graft includes an internalliner. The internal liner is described as an inelastic material and isfolded within the stent graft. Upon radial expansion of stent-graft, theinternal liner is described as further limiting the radial expansion ofthe stent-graft. Furthermore, a graft containing circumferentialcomposite yarns is described as yet another alternative for limitingradial expansion. The composite yarns are described as havinginexpansible yarns counter wound or braided over an elastic core yarn.The inexpansive yarns are described as limiting radial expansion ofgraft. These attempts to limit radial expansion of a stent-graft,however, result in complicated the stent-graft designs that have eitheradditional liners or complex composite yarn designs.

[0011] Thus, there is a need for a graft that compliments theimplantation of an expandable stent of a stent-graft endoprosthesis andlimits dilation without the disadvantages of the prior art. Inparticular, there is need for a graft that is securably attached to thestent in both the expanded and unexpanded state which limits withoutcomplicating the mechanical dynamics of the stent or the graft.

SUMMARY OF THE INVENTION

[0012] The present invention provides an implantable tubular prosthesishaving a radially expandable tubular stent structure having a firstdiameter and capable of longitudinal expansion or contraction to achievea second diameter which is different from the first diameter and atubular knitted tubular graft circumferentially disposed and securablyattached to the stent. The graft has a pattern of interlaced wale andcourse yarns in a warp knit pattern to permit longitudinal expansion orcontraction of the graft substantially consistent with the longitudinalexpansion or contraction of the stent.

[0013] The prosthesis of the present invention is capable oflongitudinal expansion from 50 to 200 percent by length from a quiescentstate. Alternatively, the prosthesis of the present invention is capableof 50 to 200 percent longitudinal contraction by length to achieve asubstantially quiescent state from an unexpanded state. Furthermore, thetextile graft of the present invention is substantially fluid-tight inits quiescent state.

[0014] To achieve such a degree of longitudinal expansion or contractionthe textile graft includes a single layer, warp knit pattern having aset yarns diagonally shifted over two or more yarns before forming aloop between engaging yarns. The knit pattern is generally described asa warp knit pattern with at least a two needle underlap. Such patternsdepart a high degree of flexibility and stretchability to the textilegraft of the present invention. Moreover, such patterns substantiallyinhibits radial expansion of the textile graft beyond a desired diameterto limit dilation of the graft.

[0015] In one aspect of the present invention an implantable tubularprosthesis is provided which is capable of longitudinal expansion from aquiescent state to an elongated state including a radially contractibleand longitudinally expandable tubular stent having a quiescent diameterand quiescent length capable of longitudinal expansion to the elongatedstate having an elongated length and a contracted diameter, wherein theelongated length is greater than the quiescent length and the contracteddiameter is smaller than the quiescent diameter. The prosthesis furtherincludes a tubular knitted tubular graft circumferentially disposed andsecurably attached to the stent in the quiescent state. The graft has asingle layer of yarns interlaced into stitches in a knit pattern capableof resilient longitudinal elongation and resilient radial contraction ofthe graft to the elongated state. The graft has from 400 to 1,000stitches per square centimeter to provide compliancy in the quiescentstate. The knit pattern is a warp knitted pattern of yarns forming atextile layer having an interior surface and an exterior surface,wherein interior yarns predominate the interior surface and form loopsin the longitudinal direction of the prosthesis, and exterior yarnspredominate the exterior surface and are diagonally shifted over two ormore of the interior yarns in an alternating pattern along a width ofthe prosthesis before engaging an interior yarn.

[0016] In another aspect of the present invention, the prosthesisincludes a longitudinally expandable stent and an expandable warpknitted graft having a single layer of yarns to define a single layeredgraft wall having a thickness from 0.3 to 0.4 millimeters. The yarns areinterlaced into stitches in a knit pattern capable of resilientlongitudinal elongation and resilient radial contraction of the graft toan elongated state. The graft has greater than 350 stitches per squarecentimeter to provide compliancy in its quiescent state. The knitpattern is a warp knitted pattern of yarns forming a textile layerhaving an interior surface and an exterior surface, wherein interioryarns predominate the interior surface and form loops in thelongitudinal direction of said prosthesis, and exterior yarnspredominate the exterior surface and are diagonally shifted over two ormore of the interior yarns in an alternating pattern along a width ofthe prosthesis before engaging an interior yarn.

[0017] In still another aspect of the present invention, the prosthesisincludes a longitudinally expandable stent and an expandable warpknitted graft having a single layer of yarns to define a single layeredgraft wall. The yarns are interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of the graft to an elongated state wherein the elongatedlength is from 50 to 200 percent by length greater than the quiescentlength. The graft has greater than 350 stitches per square centimeter toprovide compliancy in its quiescent state. The knit pattern is a warpknitted pattern of yarns forming a textile layer having an interiorsurface and an exterior surface, wherein interior yarns predominate theinterior surface and form loops in the longitudinal direction of saidprosthesis, and exterior yarns predominate the exterior surface and arediagonally shifted over two or more of the interior yarns in analternating pattern along a width of the prosthesis before engaging aninterior yarn.

[0018] In a further aspect of the present invention, the prosthesisincludes a longitudinally expandable stent and an expandable warpknitted graft having a single layer of yarns to define a single layeredgraft wall. The yarns are interlaced into stitches in a knit patterncapable of resilient longitudinal elongation and resilient radialcontraction of the graft to an elongated state. The graft has greaterthan 350 stitches per square centimeter to provide compliancy in itsquiescent state. The knit pattern is a warp knitted pattern of yarnsforming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns predominate the interior surface andform loops in the longitudinal direction of said prosthesis, andexterior yarns predominate the exterior surface and are diagonallyshifted over two or more of the interior yarns in an alternating patternalong a width of the prosthesis before engaging an interior yarn. Thestent and the graft are resiliently deformable between the quiescent andthe elongated states and the graft is capable of non-bulging contractionfrom the elongated state to the quiescent state to circumferentiallyabut the stent.

[0019] In other aspects of the present invention, a non-textile,desirably ePTFE, layer is provided with the endoprosthesis of thepresent invention. Furthermore, an implantable medical fabric isprovided. The medical fabric is a knitted textile with a high degree ofstretchability because of the warp knit pattern with at least a twoneedle underlap used to form the fabric. Moreover, a method for warpknitting a tubular graft with a warp knit pattern with at least a twoneedle underlap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a partial cut-away perspective view of an endoprosthesisof the present invention having a stent and a graft both capable oflongitudinal expansion or contraction.

[0021]FIG. 2 is a cross-sectional view of the stent-graft of FIG. 1taken along the 2-2 axis.

[0022]FIG. 3 depicts the stent-graft of FIG. 2 having a longitudinallyexpanded length.

[0023]FIG. 4 depicts a wire stent in an expanded state according to thepresent invention.

[0024]FIG. 5 depicts the wire stent of FIG. 5 in an unexpanded state.

[0025]FIG. 6 depicts a slotted stent in a quiescent state according tothe present invention.

[0026]FIG. 7 depicts the slotted-stent of FIG. 6 in an expanded state.

[0027]FIG. 8 is a perspective view of a helical coil formed of a singlewound wire.

[0028]FIG. 9 is a perspective view of a stent having an elongatepre-helically coiled configuration.

[0029]FIG. 10 is a perspective view of the stent of FIG. 9 in a radiallyexpanded state.

[0030]FIG. 11 is an illustration of a textile portion of the graft ofFIG. 1 taken along the 11-11 axis.

[0031]FIGS. 12 and 13 depict yarn patterns for the textile portion ofFIG. 8.

[0032]FIG. 14 is a cross-sectional of the present invention whichfurther includes a layer of e-PTFE.

[0033]FIG. 15 is a partial perspective view of a knitted medical fabricof the present invention.

[0034]FIG. 16 is a photomicrograph showing a longitudinally expandedePTFE structure.

[0035]FIG. 17 is a photomicrograph of physically modified ePTFEstructure having enhanced elongation properties as compared to the ePTFEstructure of FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention addresses the problems associated withprior art stent-graph endoprosthesis. The stent-graft endoprosthesis ofthe present invention overcomes the disadvantages of presently availablestent-grafts by providing an expandable graft that complements anexpandable stent in both an expanded or contracted state and thatfurther substantially inhibits dilation of the stent-graft afterimplantation into a bodily lumen. Furthermore, the graft of the presentinvention is knitted textile graft which provides a constraint againstundesirable radial expansion while also providing greater longitudinalstretchability than previously knitted or woven textile grafts.Moreover, the knitted textile graft of the present invention has aporosity to permit the ingrowth of cells for the stabilization ofimplanted endoprosthesis while also being generally impermeable toinhibit substantial leakage of blood therethrough.

[0037]FIG. 1 is a depiction of stent-graft 10 of the present invention.Stent-graft 10 is shown as a generally tubular structure with open ends16, 18 to permit the passage of a bodily fluid therethrough. Stent-graft10 includes textile graft 12 and stent 14. Textile graft 12 extendscircumferentially about stent 14. Textile graft 12 is securably attachedto stent 14. The attachment of textile graft 12 to stent 14 may beaccomplished by mechanically securing or bonding the textile graft 12and the stent 14 to one and the other. Mechanical securement includes,but is not limited to, the use of sutures, anchoring barbs, textilecuffs and the like. Bonding includes, but is not limited to, chemicalbonding, for instance adhesive bonding, thermal bonding and the like.

[0038] As depicted in FIG. 1, the textile graft 12 circumferentiallyextends about an outer stent surface 20. The present invention, however,is not so limited and other stent-graft configurations may suitably beused with the present invention. For instance, textile graft 12 may becircumferentially positioned along an inner surface of stent 14.Moreover, the longitudinal lengths of the stent 14 and the textile graft12 are not limited to substantially similar lengths as depicted inFIG. 1. For instance, textile graft 12 may be shorter than stent 14thereby leaving a portion of stent 14 without being covered by textilegraft 12.

[0039]FIG. 2 dimensionally depicts the stent-graft 10 of the presentinvention after securement within a bodily lumen (not shown) and FIG. 3dimensionally depicts the stent-graft 10′ prior to securement thereat.To navigate the stent-graft within a bodily lumen the nominal diameter,D₂, of stent-graft 10′ is smaller than the diameter, D₁, of stent-graft10. Correspondingly, the length, L₂, of stent-graft 10′ is larger thanthe length, L₁, of stent-graft 10. The textile graft 12 and the stent 14both conform to these general dimensional depictions for the navigationand securement of stent-graft 10 within a bodily lumen. The textilegraft 12 is elongated or stretched to accommodate the elongatedstent-graft 10′. Correspondingly, textile graft 12 is in a substantiallyquiescent state to accommodate the stent-graft 10 of FIG. 2. Moreover,textile graft 12 is designed not to radially expand to a diametersubstantially greater than the diameter D₁ of stent-graft 10. Such adesign substantially inhibits dilation of stent-graft 10.

[0040] Various stent types and stent constructions may be employed inthe invention. Useful stents include, without limitation, self-expandingstents and balloon expandable stents. The stents may be capable ofradially contracting or expanding, as well, and in this sense can bebest described as radially or circumferentially distensible ordeformable. Self-expanding stents include those that have a spring-likeaction which causes the stent to radially expand, or stents which expanddue to the memory properties of the stent material for a particularconfiguration at a certain temperature. Nitinol is one material whichhas the ability to perform well while both in spring-like mode, as wellas in a memory mode based on temperature. Other materials are of coursecontemplated, such as stainless steel, platinum, gold, titanium andother biocompatible metals, as well as polymeric stents.

[0041] The configuration of stent 14 may be of any suitable geometry. Asshown in FIG. 4, wire stent 22 is a hollow tubular structure formed fromwire strand 24 being arranged in what can be described as a “Z” or a“zig-zag” pattern. Wire strand 24 may be formed by, for example,braiding or spinning it over a mandrel. Alternatively, wire stent 24 maybe formed from more than one wire strand.

[0042] Wire stent 22 is capable of being radially compressed andlongitudinally extended, to yield wire stent 22′, as depicted in FIG. 5,for implantation into a bodily lumen. The degree of elongation dependsupon the structure and materials of the wire stent 22 and can be quitevaried. For example, the length of wire stent 22′ is from about 50% toabout 200% of the length of wire stent 22. The diameter of wire stent22′ may also be up to several times smaller than the diameter of wirestent 22.

[0043] In another aspect of the present invention, a slotted stent 26 isalso useful as part of the stent-graft 10. As depicted in FIG. 6,slotted stent 26 is suitably configured for implantation into a bodilylumen (not shown). Upon locating the slotted stent 26 at the desiredbodily site, slotted stent 26 is radially expanded and longitudinallycontracted for securement at the desired site. The expanded slottedstent 26′ is depicted in FIG. 7. Slotted stent 26′ is from about 50% toabout 200% greater in radial dimension as compared to slotted stent 26.

[0044] Other useful stents capable of radial expansion are depicted inFIGS. 8, 9 and 10. As depicted in FIG. 8, stent 28 is a helical coilwhich is capable of achieving a radially expanded state (not shown).Stent 29, as depicted in FIG. 9, has an elongate pre-helically coiledconfiguration as shown by the waves of non-overlapping undulatingwindings. Stent 29 is capable of being radially expanded to expandedstent 29′ as depicted in FIG. 10. These helically coiled orpre-helically stents are also useful with the practice of the presentinvention.

[0045] The textile graft 12 is a knitted textile graft. Knittinginvolves the interlooping or stitching of yarn into vertical columns(wales) and horizontal rows (courses) of loops to form the knittedfabric structure. Warp knitting is particularly useful with the textilegraft 12 of the present invention. In warp knitting, the loops areformed along the textile length, i.e., in the wale or warp direction ofthe textile. For a tubular textile, such as textile graft 12, stitchesin the axial or longitudinal direction of the tubular textile are calledwales and stitches in the axial or circumferential direction of thetubular textile are called courses.

[0046] Conventional knitted tubular grafts often had to reduce thenumber of wales per inch to reduce the tendency of a graft to dilate. Alow number of wales per inch, however, often reduces compliance of thegraft where the graft may not be fluid-tight, i.e., prevent flow ofblood therethrough, without other sealing mechanisms. Conventionalgrafts also used inelastic or a combination of inelastic and elasticyarns to limit radial expansion of a knitted textile graft. The textilegraft 12 of the present invention is not so limited. The textile graft12 uses a novel knit pattern which by itself substantially inhibitsundesirable radial expansion. Moreover, the knit pattern of the presentinvention allows for radial contraction and longitudinal elongation ofthe textile graft 12 while still providing a constraint to limit radialexpansion.

[0047] Moreover, conventional knitted tubular grafts often had to reduceor limit the number of courses per inch to obtain a flexible tubularstructure, i.e., a structure with longitudinal stretchability. Reducingthe number of courses per inch, however, opens the macroporous structureof the textile. A macroporous textile structure is not desirable as agraft because such a structure is not a fluid tight structure, i.e.,blood will flow through the graft. Similarly, if the number of wales perinch was too low, the graft would not seal blood flow. If the number ofwales per inch was too high, the graft could dilate with time. Thus,conventional grafts were limited by the total number of courses andwales per inch, which is referred to as the number of picks per squareinch or the pick size.

[0048] For example, U.S. Pat. No. 5,732,572 to Litton describes atextile tubular prosthesis in a warp-knit having a underlap of greaterthan two needle spaces to limit dilation. The prosthesis, however, islimited to a pick size of 80 to 350 stitches per square centimeter(6,400 to 2,260 stitches per square inch) to provide a longitudinallystretchable tubular structure. Such a pick size represents about 9 to 19courses or wales per centimeter (23 to 48 courses or wales per inch).With such a low pick size the prosthesis of this patent is knitted inmultiple layers to provide a fluid tight structure while maintainingsome degree of stretchability and resistance to dilation. The textilegraft 12 of the present invention is not so limited because of the novelknit pattern used to form the graft as compared to more conventionalknit patterns, such as tricot, locknit and the like, or even otherstretchable knit patterns interlaced with these patterns.

[0049] Moreover, grafts are sometimes crimped with creases or foldswhich tend to reduce kinking when the graft is bent. The kinking alsoallows for some elongation of the graft, but such a crimped graft wouldnot be generally useful as a stent-graft because of the gaps that wouldresult between the stent and the crimped graft.

[0050] The textile graft 12 is configured to have a high degree ofstretchability. As used herein, the term stretchability and its variantsrefers to a textile capable of substantially reversible elongationbetween a quiescent state and a stretched state. Desirably, thestretchability of the textile graft 12 is substantially compatible withthe dimensional changes associated with an expandable stent having botha expanded and an unexpanded or a contracted state as discussed above.Moreover, textile graft 12 is not a crimped graft and does non-bulginglycontract from the elongated state to the quiescent state. The textilegraft 12 substantially abuts the stent along both circumferential andlongitudinal portions of the stent without separating or bulging fromthe stent.

[0051] Knitting patterns useful in providing desirable limits to radialexpansion while maintaining the desired longitudinal stretchabilityinclude those knitting patterns that are not highly interlaced, such aspatterns that interlace each adjacent back and front yarn. An example ofa highly interlaced and commonly known knitted pattern is a Tricot orJersey pattern. In contrast the knitting pattern of the presentinvention is not highly interlaced to provide, among other things, thestretchability of the textile graft for use with an expandable stent.

[0052]FIG. 11 is an illustration of portion 30 of textile graft 12 takenalong the 11-11 axis. The knitted portion 30 is characterized as a threeneedle underlap. In FIG. 11, needle positions in the course direction,i.e., vector 51, are noted by element numbers 32 a through 32 i andneedle positions in the wale direction, i.e., vector 53, are noted byelement numbers 34 a through 34 i. Yarn 36 a travels in the coursedirection from needle position 32 a to needle position 32 d, or threeneedle positions, before interlooping with yarn 36 d. Yarn 36 a thentravels three needle positions in the opposite course direction tointerloop with a yarn. This alternating three needle position movementis repeated with different yarns to form a knitted pattern with a threeneedle underlap.

[0053] The knitted portion 30 is depicted as a single knitted layer inFIG. 11, however, the textile graft 12 of the present invention is notso limited. For instance, the knitted portion 30 may include more thanone layer of interconnected yarns. In such a multi-layered knittedtextile, yarns from one layer are often interlooped with yarns inanother layer to form the multi-layered knitted textile.

[0054] Textile graft 12 is a flat-knitted tubular structure. To formsuch a flat-knitted tubular structure, two portions 30 are co-knittedand connected to one and the other joined together by border yarns.

[0055]FIG. 12 depicts the yarn patterns of FIG. 11 by separating thefront, back and border yarns from one and the other to more clearlyillustrate the individual yarn knit pattern and the repeating nature, ifany, of these individual yarn knit patterns. As depicted in FIG. 12,front yarn 52 and back yarn 50 are repeated about 8 times. Border yarns54 and 56 alternately repeat about three between the repeating front andback yarn patterns. The front yarn pattern is repeated to yield thetechnical front or the exterior surface of the textile graft 10 of thepresent invention. The back yarn pattern is repeated to yield thetechnical back or the interior surface of the textile graft 10 of thepresent invention.

[0056] The knitting patterns for the front and back yarns are furtherillustrated in FIG. 13. The front, back and border yarns are interlacedin a relatively loose pattern having an underlap of at least threeneedle positions, which are depicted as dots 58. As used herein the termunderlap and its variants refer to a yarn that traverses one or moreyarns before forming an interlacing loop with a yarn. Such a pattern notonly provides stretchability to the textile graft 12 but also providesresistance against dilation. Not wishing to be bound by any particulartheory, it is believed that the long underlap in the course direction,which is indicated as vector 51, reduces the potential for expansion inthe wale direction, which is indicated by vector 53, because theunderlap in the course direction inhibits undesirable radial expansion.

[0057] As shown in FIG. 13, back yarns 50 and front yarns 52 shiftdiagonally by at least three needle positions in alternating closed-loopinterlacing structures. As used herein, closed-loops refer tointerlacing yarns where a front or a back yarn crosses over itself informing the loop. Other patterns useful with the practice of the presentinvention, such as border patterns, are illustrated in FIG. 13.

[0058] To knit textile patterns useful with the present invention,double needle bar warp-knitting machine with multiple beams or guidebars is used to form a flat-knitted seamless tubular structure. Thethreading pattern for each guide bar is shown below in Table 1, and thearrangement of each needle for the guide bar is shown below in Table 2.TABLE 1 Guide Bar Threading Details Guide Bar y - Threaded/n - NotThreaded Settings 8 y y y y y y y y n n n 7 y n n n n n n n n n n 6 n nn n n n n n n n y 5 y n n n n n n n n n n 4 n n n n n n n n n y n 3 y nn n n n n n n n n 2 y n n n n n n n n n n 1 y y y y y y y y n n n

[0059] TABLE 2 Guide Bar Positions Guide Bar Positions 16-8-4-4/2-0-4-4/(repeat) Front Full Thread 8 4-4-2-0/4-4-6-8/(repeat)Back Full Thread 2 4-6-2-2/0-0-0-2/(repeat) Right Connect 42-4-0-0/2-2-2-4/(repeat) Right Connect 6 0-2-2-2/4-4-4-6/(repeat) RightConnect 3 2-2-2-0/6-4-4-4/(repeat) Left Connect 54-4-4-2/4-2-6-6/(repeat) Left Connect 7 6-6-6-4/2-0-4-4/(repeat) LeftConnect

[0060] The knitted textile graft of the present invention is desirablymade on a warp-knitting machine (not shown) using a double needle bar. Auseful number of needles per inch for warp knitting is from about 18 toabout 36. About 28 needles per inch are particularly suitable. Thetrellis of the graft is usually made from a yarn having count from 30 to300 denier. Desirably, the range of yarn counts for the trellis is fromabout 30 to about 80. A particularly suitable yarn count is about 40denier. Moreover, the trellis yarn may be a single ply, a double ply ora multi-ply. The term “multi-ply” is used herein to indicate more thantwo-ply.

[0061] Furthermore, the knitted textile graft of the present inventionhas greater than 350 stitches per square centimeter, for instance fromabout 400 to about 1,000 stitches per square centimeter (about 2,600 toabout 6,500 stitches per square inch), to provide compliancy of thegraft. Desirably, the present invention has from about 650 to about 800stitches per square centimeter (about 4,200 to about 5,200 stitches persquare inch). Moreover, the knitted textile graft of the invention hasfrom about 15 to about 50 courses or wales per centimeter (about 40 toabout 130 courses or wales per inch) to provide compliancy of the graft.The number of courses and wales per unit length may be the same ordifferent. Desirably, the present invention has from about 20 to about50 wales per centimeter (about 50 to about 130 wales per presentinvention has from about 15 to about 32 courses per centimeter (about 40to about 80 courses per inch).

[0062] In one aspect of the present invention, the knitted textile graftis a knit structure of a single layer with at least a two-needleunderlap. Because of the single layer construction the textile wallthickness is minimized to yield a low profile knitted textile graft. Thetextile wall thickness is from about 0.3 to about 0.4 millimeters.Desirably, the textile wall thickness is from about 0.33 to about 0.36millimeters. Furthermore, the knitted textile graft of the presentinvention has a burst strength from about 12 kg/cm² to about 16 kg/cm²(about 160 psi to about 220 psi). Desirably, the knitted textile graftof the present invention has a burst strength from about 13 kg/cm² toabout 14 kg/cm² (about 180 psi to about 200 psi). The stretchability ofthe knitted textile graft is 50 to 200 percent at a one-kilogram ofload. Knitted textile grafts with a stretchability of about 80 to 200percent at one-kilogram load are also useful. Furthermore, knittedtextile grafts with a stretchability of about 120 to 160 percent atone-kilogram load are also useful.

[0063] In a typical method of warp knitting the back yarn is fed fromtwo inside beams, each beam being a spool holding a plurality of ends.Outside beams may be used in conjunction with the inside beams; theoutside beams being used for feeding the front yarns. Each outside beamalso has a plurality of ends. It should be noted, however, that theinside beams may be used for feeding the front yarn and the outsidebeams used for feeding the back yarn. Regardless of which beams areused, texturized flat yarn is generally used for both the front and backyarns. The minimum number of beams used in making the textile graft ofthe present invention is 2. A greater number of beams, however, may befound useful for specific applications. Eight guide beams or guide barshave been found to be particularly useful with the practice of thepresent invention.

[0064] Any type of textile product can be used as yarns for the knittedtextile graft of the present invention. Of particular usefulness informing the knitted fabric prosthesis of the present invention aresynthetic materials such as synthetic polymers. Synthetic yarns suitablefor use in the present invention include, but are not limited to,polyesters, including PET polyesters, polypropylenes, polyethylenes,polyurethanes and polytetrafluoroethylenes. The yarns may be of themonofilament, multifilament, spun type or combinations thereof. Theyarns may also be flat, twisted or textured, and may have high, low ormoderate shrinkage properties or combinations thereof.

[0065] The yarns used in forming the textile grafts of the presentinvention may be flat, twisted, textured or combinations thereof.Furthermore, the yarns may have high, low or moderate shrinkageproperties or combination of different shrinkage properties.Additionally, the yarn type and yarn denier can be selected to meetspecific properties desired for the prosthesis, such as porosity andflexibility. The yarn denier represents the linear density of the yarn(number of grams mass divided by 9,000 meters of length). Thus, a yarnwith a small denier would correspond to a very fine yarn whereas a yarnwith a larger denier, e.g., 1000, would correspond to a heavy yarn. Theyarns used with the present invention may have a denier from about 20 toabout 200, preferably from about 30 to about 100. Preferably, the yarnsare polyester, such as polyethylene terephthalate (PET), and morepreferably the yarns are one ply, 40 denier, 27 filament flat andtexturized polyester.

[0066] After knitting the textile graft of the present invention isoptionally cleaned or scoured in a basic solution of warm water, e.g.,about 50° C. to about 65° C. (about 120° F. to about 150° F.), anddetergent. The textile is then rinsed to remove any remaining detergent.

[0067] After the textile graft is optionally scoured, the graft iscompacted or shrunk to reduce and control, in part, the porosity of thegraft. Porosity of a knitted material is measured on the Wesolowskiscale and by the procedure of Wesolowski. In the Wesolowski test, afabric test piece is clamped flatwise and subjected to a pressure headof about 120 mm. of mercury. Readings are obtained which express thenumber of millimeters of water permeating per minute through each squarecentimeter of fabric. A zero reading represents absolute waterimpermeability and a value of about 20,000 represent approximate freeflow of fluid.

[0068] The porosity of the textile graft 12 is often from about 7,000 toabout 15,000 on the Wesolowski scale after being knitted on the doubleneedle bar Raschel knitting machine. A more desirable porosity is fromabout 30 to about 5,000 on the Wesolowski scale and textile graft iscompacted or shrunk in the wale direction to obtain the desiredporosity. A solution of an organic component, such ashexafluoroisopropanol or trichloroacetic acid, and a halogenatedaliphatic hydrocarbon, such as methylene chloride, is used to compactthe textile graft by immersing it into the solution for up to 30 minutesat temperatures from about 15° C. to about 160° C. Other compactingsolutions may suitably be used, such as those disclosed in U.S. Pat.Nos. 3,853,462 and 3,986,828, whose contents are incorporated byreference herein.

[0069] As noted above, preferably the tubular-knitted graft of thepresent invention is constructed of polyester which is capable ofshrinking during a heat-set process. For instance, such grafts aretypically flat-knitted in a tubular form. Due to the nature of theflat-knitting process, the tubular graft is generally flat in shapeafter knitting. Such grafts, however, when constructed of shrinkablepolyester yarn, can be heat set on a mandrel to form a generallycircular shape.

[0070] Such a heat-setting process is accomplished by first knitting thegraft in a seamless tubular form out of a material capable of shrinkingduring a heat-setting or similar process. The graft may be preshrunkbefore it is placed on a mandrel. Preshrinking may be achieved bysubmitting the woven graft to moderate temperatures, such as from about90° C. to about 205° C. (about 190° F. to about 400° F.). Usually thegraft is placed in a medium for the preshrinking. Such a medium caninclude without limitation hot water, a chemical fluid, such asmethylene chloride, or a gas, such as air or carbon dioxide. The graftof the present invention, however, may suitably be made without such apreshrinking of the yarns.

[0071] After the graft is knitted or alternatively knitted andpreshrunk, the graft is placed on a mandrel, and heated in an oven at atemperature and time capable of causing the yarns of the graft to heatset to the shape and diameter of the mandrel. Preferably polyester yarnsare used, and the heat setting is accomplished at time and temperaturesappropriate for the material. For example, heat setting can beaccomplished at about 90° C. to about 225° C. (about 190° F. to about437° F.) for a period of about less than an hour. Temperatures in therange of about 130° C. to about 220° C. (about 260° F. to about 428° F.)are also useful. Desirably, temperatures from about 150° C. to about215° C. (about 300° F. to about 419° F.) are also useful. Desirably,time periods from about 5 to about 30 minutes are useful. Moredesirably, with time periods from about 10 to about 20 minutes areuseful. Other methods of heat setting known in the art may be employed.After such a heat setting process, the graft can be formed into a shapedesired for implantation, having a generally circular inner lumen.

[0072] In another aspect of the present invention stent-graft 10 furtherincludes a non-textile layer 13, as depicted in FIG. 14. The non-textilelayer is circumferentially disposed between textile graft 12 and stent14 and securably attached therebetween. One type of non-textile materialparticularly useful is polytetrafluoroethylene (PTFE). PTFE exhibitssuperior biocompatibility and low thrombogenicity, which makes itparticularly useful as vascular graft material in the repair orreplacement of blood vessels. Desirably the non-textile layer is atubular structure manufactured from expanded polytetrafluoroethylene(ePTFE). The ePTFE material has a fibrous state which is defined byinterspaced nodes interconnected by elongated fibrils. The space betweenthe node surfaces that is spanned by the fibrils is defined as theinternodal distance. When the term expanded is used to describe PTFE, itis intended to describe PTFE which has been stretched, in accordancewith techniques which increase the internodal distance and concomitantlyporosity. The stretching may be in uni-axially, bi-axially, ormulti-axially. The nodes are spaced apart by the stretched fibrils inthe direction of the expansion.

[0073] Desirably, the ePTFE material is a physically modified ePTFEtubular structure having enhanced axial elongation and radial expansionproperties of up to 600 percent by linear dimension. The physicallymodified ePTFE tubular structure is able to be elongated or expanded andthen returned to its original state without an elastic force existingtherewithin. Such a physically modified ePTFE tubular structure isadvantageously used in conjunction with wire-stent 22 of stent-graft 10.

[0074]FIG. 16 is a photomicrograph of a traditionally longitudinallyexpanded ePTFE tubular structure. The tube has been stretched in thelongitudinal direction shown by directional arrow 102, leaving the nodescircumferentially oriented in circumferential direction shown by thedirectional arrow 104. The fibrils 106 are shown as being uniformlyoriented in the longitudinal direction shown by directional arrow 102.Nodes 108 are shown and are uniformly oriented in circumferentialdirection 104.

[0075]FIG. 17 is a photomicrograph of the physically modified ePTFEtubular structure having circumferentially oriented nodes andlongitudinally traversing fibrils. Nodes 110 are shown in thephotomicrograph with a set of fibrils with first ends 112 and secondends 114 attached thereto. The fibrils with first ends 112 and secondends 114 are shown in a hingeably rotated position so that they are notsubstantially longitudinally oriented in the direction shown bydirectional arrow 102 as compared to the substantially longitudinallyoriented parallel fibril structures 106 of FIG. 13. The term “hingeablyrotated” and variants thereof refer to reorientation of previouslyuniformly oriented line segments by a change in position of one end ofeach line segment in relation to the other end of each segment, whichremains fixed; i.e., the “hinge” about which the other end rotates. Thereorientation takes place without a substantial change in dimension ofthe line segment. Additional details of the physically-modified ePTFEand methods for making the same can be found in commonly assignedapplication titled, “ePTFE Graft With Axial Elongation Properties”,filed on date herewith, attorney docket 498-256, the contents of whichare incorporated by reference herein.

[0076]FIG. 15 is a partial perspective view of an implantable medicalfabric 40, another aspect of the present invention. The medical fabric40 is a warp-knitted textile fabric having at least a two needleunderlap as described above. The medical fabric 40 has the features ofthe above-described textile graft 12, for instance, a high degree ofstretchability. The medical fabric 40 of the present invention is usefulin intraluminal applications, such as hernia repair.

[0077] The invention may be further understood with reference to thefollowing non-limiting examples.

EXAMPLES Example 1. Single Layer Knit Tubular Graft With a Three NeedleUnderlap

[0078] The following specifications are used to fabricate a solidknitted prosthesis of the present invention.

[0079] Yarn Type: Texturized polyethylene terephthalate (PET), 40denier, 27 filaments.

[0080] Machine Type: 56 Guage Kidde machine.

[0081] Number of Guide Bars: Eight

[0082] Guide Bar Threading Details: (y-Threaded/n-Not Threaded)

[0083] Guide Bar No. 8: y/y/y/y/y/y/y/y/n/n/n

[0084] Guide Bar No. 7: y/n/n/n/n/n/n/n/n/n/n

[0085] Guide Bar No. 6: n/n/n/n/n/n/n/n/n/n/y

[0086] Guide Bar No. 5: y/n/n/n/n/n/n/n/n/n/n

[0087] Guide Bar No. 4: n/n/n/n/n/n/n/n/n/y/n

[0088] Guide Bar No. 3: y/n/n/n/n/n/n/n/n/n/n

[0089] Guide Bar No. 2: y/n/n/n/n/n/n/n/n/n/n

[0090] Guide Bar No. 1: y/y/y/y/y/y/y/y/n/n/n

[0091] Guide Bar Position Details:

[0092] Guide Bar No. 1: 6-8-4-4/2-0-4-4/(repeat) Front Full Thread

[0093] Guide Bar No. 8: 4-4-2-0/4-4-6-8/(repeat) Back Full Thread

[0094] Guide Bar No. 2: 4-6-2-2/0-0-0-2/(repeat) Right Connect

[0095] Guide Bar No. 4: 2-4-0-0/2-2-2-4/(repeat) Right Connect

[0096] Guide Bar No. 6: 0-2-2-2/4-4-4-6/(repeat) Right Connect

[0097] Guide Bar No. 3: 2-2-2-0/6-4-4-4/(repeat) Left Connect

[0098] Guide Bar No. 5: 4-4-4-2/4-2-6-6/(repeat) Left Connect

[0099] Guide Bar No. 7: 6-6-6-4/2-0-4-4/(repeat) Left Connect

[0100] Graft Processing:

[0101] Subsequent to knitting the textile graft, the material is scouredin a basic solution of warm water (e.g., about 65° C. or about 150° F.)and cleaning detergent. It is then rinsed to remove the cleaning agents.The graft is then compacted with methylene chloride at elevatedtemperatures, for instance about 107° C. or about 224° F., for a shortperiod of time, for instance, three minutes.

[0102] Next, the prosthesis is heat-set on stainless steel mandrels toachieve the final desired inside diameter. Typically, the outsidediameter of the mandrel is typically twenty to forty percent oversizedto impart, in part, high stretch and low dilation characteristics to thetextile graft. Heat setting can take place in a convection oven at about212° C. (about 414° F.) for about 10 minutes.

[0103] As a result of the heat setting, the warp yarns are locked in theknitted geometry with a three-needle underlap to build in “spring like”properties that capable of longitudinal expansion. The heat set graft iscapable of about 50 to 200 percent longitudinal expansion.

Example 2 Single Layer Stretch Knit Straight Tubular Graft with aTwo-Needle Underlap

[0104] The following specifications were used to fabricate a superstretch knitted prosthesis of the present invention.

[0105] Yarn Type Used: Texturized polyethylene terephthalate (PET), 40denier, 27 filaments.

[0106] Machine Used: 56 gauge Kiddie machine

[0107] Guide Bars Used: 6 Guide Bar Threading Details: (y - threaded,n - not threaded): Guide Bar n n y y y y y y y y y n No. 6 Guide Bar n yn n n n n n n n n n No. 5 Guide Bar n n n n n n n n n n n y No. 4 GuideBar n n n n n n n n n n y n No. 3 Guide Bar y n n n n n n n n n n n No.2 Guide Bar n n y y y y y y y y y n No. 1

[0108] Guide Bar Chain Notation Details: Guide Bar No. 1:2-0/4-4/4-6/2-2//repeat Front full thread Guide Bar No. 2:4-2/4-4/2-2/2-0//repeat Left connector Guide Bar No. 3:2-2/2-4/0-2/0-0//repeat Right connector Guide Bar No. 4:0-0/0-2/2-4/2-2//repeat Right connector Guide Bar No. 5:2-0/2-2/4-4/4-2//repeat Left connector Guide Bar No. 6:2-2/4-6/2-2/2-0//repeat Back full thread

[0109] Graft Processing:

[0110] Subsequent to knitting the textile graft, the material wasscoured in a basic solution of warm water (e.g., about 65° C. or about150° F.) and cleaning detergent. It was then rinsed to remove thecleaning agents. The graft was then compacted with methylene chloride atelevated temperatures, for instance about 107° C. or about 224° F., fora short period of time, for instance, three minutes.

[0111] Next, the prosthesis was heat-set on stainless steel mandrels toachieve the final desired inside diameter. Typically, the outsidediameter of the mandrel was twenty to forty percent oversized to impart,in part, high stretch and low dilation characteristics to the textilegraft. Heat setting was accomplished in a convection oven at about 212°C. (about 414° F.) for about 10 minutes.

[0112] As a result of the heat setting, the warp yarns were locked inthe knitted geometry with a two-needle underlap to build in “springlike” properties that capable of longitudinal expansion. The heat setgraft was capable of about 50 to 200 percent longitudinal expansion.

Example 3 Single Layer Stretch Knit Bifurcated Tubular Graft with a TwoNeedle Underlap

[0113] The following specifications were used to fabricate a bifurcatedsuper stretch knitted prosthesis of the present invention.

[0114] Yarn Type Used: Texturized polyethylene terephthalate (PET), 40denier, 27 filaments.

[0115] Machine Used: 56 gauge Kiddie machine

[0116] Guide Bars Used: 10 Guide Bar Threading Details: (y - threaded,n - not threaded): Guide Bar n n y y y y n n y y y y n No. 10 Guide Barn y n n n n n n n n n n n No. 9 Guide Bar n n n n n n n n n n n n y No.8 Guide Bar n n n n n n y n n n n n n No. 7 Guide Bar n n n n n n n n yn n n n No. 6 Guide Bar n n n n n n n y n n n n n No. 5 Guide Bar n n nn n n n y n n n n n No. 4 Guide Bar n n n n n n n n n n n y n No. 3Guide Bar y n n n n n n n n n n n n No. 2 Guide Bar n n y y y y n n y yy y n No. 1

[0117] Guide Bar Chain Notation Details: Guide Bar No. 1:2-0/4-4/4-6/2-2//repeat Front full thread Guide Bar No. 2:4-2/4-4/2-2/2-0//repeat Left connector Guide Bar No. 3:2-2/2-4/0-2/0-0//repeat Right connector Guide Bar No. 4 Leg:4-4/4-2/2-0/2-2//repeat Bifurcation connector Guide Bar No. 4 Body:4-6/2-2/2-0/4-4//repeat Join Bar No. 1 Guide Bar No. 5 Leg:4-6/4-4/2-2/2/4//repeat Bifurcation connector Guide Bar No. 5 Body:4-6/2-2/2-0/4-4//repeat Join Bar No. 1 Guide Bar No. 6 Leg:2-4/2-2/4-4/4-6//repeat Bifurcation connector Guide Bar No. 6 Body:2-2/2-0/4-4/4-6//repeat Join Bar No. 10 Guide Bar No. 7 Leg:2-2/2-0/4-2/4-4//repeat Bifurcation connector Guide Bar No. 7 Body:2-2/2-0/4-4/4-6//repeat Join Bar No. 10 Guide Bar No. 8:0-0/0-2/2-4/2-2//repeat Right connector Guide Bar No. 9:2-0/2-2/4-4/4-2//repeat Left connector Guide Bar No. 10:2-2/4-6/2-2/2-0//repeat Back full thread

[0118] Graft Processing:

[0119] Subsequent to knitting the textile graft, the material wasscoured in a basic solution of warm water (e.g., about 65° C. orabout-150° F.) and cleaning detergent. It was then rinsed to remove thecleaning agents. The graft was then compacted with methylene chloride atelevated temperatures, for instance about 107° C. or about 224° F., fora short period of time, for instance, three minutes.

[0120] Next, the prosthesis was heat-set on stainless steel mandrels toachieve the final desired inside diameter. Typically, the outsidediameter of the mandrel was twenty to forty percent oversized to impart,in part, high stretch and low dilation characteristics to the textilegraft. Heat setting was accomplished in a convection oven at about 212°C. (about 414° F.) for about 10 minutes.

[0121] As a result of the heat setting, the warp yarns were locked inthe knitted geometry with a two-needle underlap to build in “springlike” properties that capable of longitudinal expansion. The heat setgraft was capable of about 50 to 200 percent longitudinal expansion.

[0122] Although illustrative embodiments of the present invention havebeen described herein with reference to the accompanying drawings, it isto be understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention.

What is claimed is:
 1. An implantable tubular graft comprising: atubular knitted tubular graft comprising a single layer of yarns todefine a single layered wall, said yarns being interlaced into stitchesin a knit pattern capable of resilient longitudinal elongation andresilient radial contraction of said graft from a quiescent state to anelongated state; wherein said knit pattern is a warp knitted pattern ofyarns forming a textile layer having an interior surface and an exteriorsurface, wherein interior yarns comprise the interior surface and formloops in the longitudinal direction of said graft, and exterior yarnscomprise the exterior surface and are diagonally shifted over two ormore of the interior yarns in an alternating pattern along a width ofsaid graft before engaging an the interior yarn.
 2. The graft of claim 1wherein the elongated length is at least 50 percent by length greaterthan the quiescent length; and further wherein the elongated length isno more than about 200 percent by length greater than the quiescentlength.
 3. The graft of claim 1 wherein said graft has at least 350stitches per square centimeter.
 4. The graft of claim 1 wherein saidgraft has at least 400 stitches per square centimeter; and furtherwherein said graft has no more than about 1,000 stitches per squarecentimeter.
 5. The graft of claim 1 wherein said graft is substantiallyfluid-tight in the quiescent state.
 6. The graft of claim 1 wherein saidexterior yarns are diagonally shifted over from three to five of theinterior yarns.
 7. The graft of claim 1 wherein said diagonally shiftedyarns inhibit radial expansion of said graft to diameters greater thanthe quiescent diameter.
 8. The graft of claim 1 wherein said singlelayer of yarns form a graft wall having a thickness of about at least0.3 millimeters.
 9. The graft of claim 1 wherein single layer of yarnsform a graft wall having a thickness of no more than about 0.4millimeters.
 10. The graft of claim 1 wherein said wall comprises anumber of tubular legs.
 11. The graft of claim 10 wherein said number oftubular legs is two to define a bifurcated graft.
 12. The graft of claim1 further including a tubular layer of PTFE circumferentially disposedand securably attached to said graft.
 13. The graft of claim 12 whereinsaid tubular layer of PTFE is a tubular layer of ePTFE.
 14. The graft ofclaim 1 wherein said yarns are selected from the group consisting ofmonofilament yarns, multifilament yearns, spun type yarns, flat yarns,twisted yarns, textured yarns, and combinations thereof.
 15. The graftof claim 1 wherein said yarns are selected from the group of materialsselected from polyesters, polypropylenes, polyethylenes, polyurethanes,polytetrafluoroethylenes or combinations thereof.
 16. The graft of claim15 wherein said polyesters include polyethylene terephthalatepolyesters.
 17. An implantable tubular graft comprising: a tubularknitted tubular graft comprising a layer of yarns to define a wall, saidyarns being interlaced into stitches in a knit pattern capable ofresilient longitudinal elongation and resilient radial contraction ofsaid graft from a quiescent state to an elongated; wherein said knitpattern is a warp knitted pattern of yarns forming a textile layerhaving an interior surface and an exterior surface, wherein interioryarns comprise the interior surface and form loops in the longitudinaldirection of said graft, and exterior yarns comprise the exteriorsurface and are diagonally shifted over two or more of the interioryarns in an alternating pattern along a width of said graft beforeengaging an the interior yarn.
 18. The graft of claim 17 wherein saidyarns are interlaced into a number of stitches from about 400 stitchesper square centimeter to about 1,000 stitches per square centimeter toprovide compliancy in the quiescent state.
 19. The graft of claim 17wherein said exterior yarns are diagonally shifted over from three tofive of the interior yarns.
 20. The graft of claim 17 wherein said layerof yarns form a graft wall having a thickness of at least about 0.3millimeters.
 21. The graft of claim 17 wherein said layer of yarns forma graft wall having a thickness of no more than about 0.4 millimeters.22. The graft of claim 17 wherein said wall comprises a number oftubular legs.
 23. The graft of claim 22 wherein said number of tubularlegs is two to define a bifurcated graft.
 24. The graft of claim 17wherein the longitudinal expansion is at least about 50 percent bylength of the length in the quiescent state; and further wherein thelongitudinal expansion is no more than about 200 percent by length ofthe length in the quiescent state.
 25. The graft of claim 17 whereinsaid graft has a substantially fluid-tight quiescent state.
 26. Thegraft of claim 17 wherein said yarns are selected from the groupconsisting of monofilament yarns, multifilament yearns, spun type yarns,flat yarns, twisted yarns, textured yarns, and combinations thereof. 27.The graft of claim 17 wherein said yarns are selected from the group ofmaterials selected from polyesters, polypropylenes, polyethylenes,polyurethanes, polytetrafluoroethylenes or combinations thereof.
 28. Thegraft of claim 27 wherein said polyesters include polyethyleneterephthalate polyesters.
 29. The graft of claim 17 wherein said patternhas at least about 20 stitches per centimeter in the longitudinaldirection of the graft; and further wherein said pattern has no morethan about 50 stitches per centimeter in the longitudinal direction ofthe graft.
 30. An implantable device comprising: a textile structurehaving a single layer of yarns to define a tubular wall having a firstsurface and a second opposed surface, wherein a first yarn comprises thefirst surface and forms loops in the longitudinal direction of saidstructure, and a second yarn comprises the second surface and isdiagonally shifted over two or more of the first yarns in an alternatingpattern along a width of said structure before engaging the first yarnto permit longitudinal expansion of at least about 50 percent by lengthof the length of said structure.
 31. An implantable device comprising: atextile structure having a single layer of yarns interlaced intostitches in a knit pattern capable of resilient longitudinal expansionfrom a quiescent state and having at least about 400 stitches per squarecentimeter and further having no more than about 1,000 stitches persquare centimeter to provide compliancy for the structure; wherein saidknit pattern is a warp knitted pattern of yarns forming a textile layerhaving a first surface and a second opposed surface, wherein a firstyarn comprises the first surface and forms loops in the longitudinaldirection of said fabric, and a second yarn comprises the second surfaceand is diagonally shifted over two or more of the first yarns in analternating pattern along a width of said fabric before engaging thefirst yarn, and further wherein said textile structure is a tubulargraft structure or a medical fabric structure.
 32. A knitted medicalfabric comprising: a knitted structure having a single layer of yarnsinterlaced into stitches in a knit pattern capable of resilientlongitudinal expansion from a quiescent state and having at least about400 stitches per square centimeter and further having no more than about1,000 stitches per square centimeter to provide compliancy for thestructure; wherein said knit pattern is a warp knitted pattern of yarnsforming a textile layer having a first surface and a second opposedsurface, wherein a first yarn comprises the first surface and formsloops in the longitudinal direction of said fabric, and a second yarncomprises the second surface and is diagonally shifted over two or moreof the first yarns in an alternating pattern along a width of saidfabric before engaging a the first yarn.
 33. The medical fabric of claim32 wherein the longitudinal expansion is at least about 50 percent bylength of the quiescent length; and further wherein the longitudinalexpansion is no more than about 200 percent by length of the quiescentlength.
 34. The medical fabric of claim 32 wherein said graft has asubstantially fluid-tight quiescent state.
 35. The medical fabric ofclaim 32 wherein said yarns are polyethylene terephthalate polyestertextured yarns having a denier of at least 30; and further wherein saidpolyethylene terephthalate polyester textured yarns have a denier toabout 80.